Factors Of Soil Formation And Their Evolution In The South Of The Zerafshan Valley

Annotation. In article is stated main groundforming (the geomorphological-hydra geological land reclamation, climatic and anthropogen) factors, describes the evolution of soils in the lower part. In Zerafshan valley are chosen 3 geomorphological regions. Differ the raised contents a magnesium, high water table on irrigated territory in roast time and heavy expences them on evaporation. Economic activity of the person is reflected and on climate, and on hydralogical condition to surfaces of the land. As a result of reclamation measures, takyr-meadow, old-fallow meadow with bog-meadow and salt marshes, gray-brown soils were transformed into old-irrigated meadow alluvial soils. The increase in irrigated land was due to the development of new, previously unrevealed territories.

Floodplain, I and II above-floodplain terraces of the Zerafshan River, composed of layered alluvial deposits.
II. The zone of light gray soils. The sub-mountain sloping plain, coupled with the IV-V terraces of the Zerafshan River, is composed of proluvial loess-like and skeletal-fine-grained deposits. The third terrace of the Zarafshan River, composed of alluvial-proluvial deposits. I and II above-floodplain terraces of the Zerafshan River, composed of layered alluvial deposits.
III. Desert zone. Ancient Peripheral Plain (Ancient the outflow cone of the Zerafshan River), composed of proluvial-alluvial deposits. The upper and middle parts of the inner modern Bukhara delta of the Zerafshan River, composed of proluvial-alluvial deposits. The lower part of the inner modern Bukhara delta of the Zerafshan River, composed of proluvialalluvial deposits. Floodplain, I and II above-floodplain terraces of the Zarafshan River, composed of layered alluvial deposits.
Karakul part of the Zerafshan River delta, composed of layered alluvial deposits. The irrigation zone of the Samarkand region covers flat areas represented by sub-mountain slopes associated with the V and IV terraces of the Zerafshan River, as well as its low terraces, which are most intensively used for irrigated agriculture. Foothill sloping plains, coupled with the upper terraces of the Zerafshan River, border the Samarkand part of the Zerafshan Valley with a wide strip. Their geomorphological heterogeneity is determined mainly by the genesis of soil-forming rocks.
The sub-mountain proluvial plains are represented by completely flat or wide-undulating spaces.
Their development is due both to the accumulation of sediments of temporary, mainly non-oil water flows flowing down from the mountains surrounding the plains, and to the ancient, now deforested, deposits of Praserafshan.
The soil-forming rocks within the foothill plains and high terraces are proluvial skeletal-fine-grained and loess-like indistinctly layered deposits. The foothill areas have quite favorable relief conditions for irrigated agriculture.
The upper level of the most ancient irrigation zone is formed by the III above-flood alluvial-proluvial terrace. It is separated from the alluvial plain by a cliff up to 15-20 m, smoothed in places. The structure of its surface is quite simple, especially in the eastern half of the valley. Shirokoformatnaya sloping the flat surface only in some places cut through by ravines. Thick strata of weakly layered loess-like loams are overlain over large areas by cultural and irrigation loam deposits reaching a thickness of 2-3 m. The first and especially the second terraces of Zarafshan form a vast alluvial plain, reaching within the Samarkand oasis in a diameter of 10-20 km. In Bukhara Oasis II, the terrace occupies the predominant part of the delta. The flatness of the relief is broken here only by artificial mounds, adjacent ramparts, and on the first terraceby the dry beds of the former channels of the river. In some places, the "cup" relief characteristic of ancient oases is formed.
Pebble accumulations at the base of the alluvial plain reach tens and hundreds of meters. They are underlain by Neogene deposits, and in the surface horizons they are overlain by fine-grained sediments of variegated mechanical composition and different thickness: on the first terrace -0.5-3 m, on the secondup to 3-5 m.
According to the research of A. I. Shevchenko [1], the foothill plains bordering the eastern part of the Samarkand basin are intensively drained by the river. Fresh ground water here lies at a depth of 5-6 to 17-18 m. Irrigation and development of the foothill plains for irrigated agriculture is accompanied by changes in hydrogeological conditions. Ground water in the territory with a slow outflow rises to 2-3 m from the ground surface.
The territory of the western part of the Zerafshan Valley within the Samarkand region is characterized by a higher occurrence of groundwater and increased mineralization, although the Zerafshan riverbed drains the adjacent massifs here as well. In the areas of the ancient and modern valleys of the Zerafshan River (from the village of Khatyrchi to the meridian of Ziaetdin-Kermine), groundwater lies at a depth of 1-3 (5) m, sometimes wedged to the surface. Due to local water stops, they are locally stagnant. Mineralization 2-3 g / L, sometimes 3-5-10 g/L. With the advance along the valley to the border with the Bukhara oasis, the groundwater level changes from 2-7 to 1-2 m. Their mineralization increases to 5-10 or more g / L, which determines the severe reclamation condition of the territory. Filtration water from canals and irrigated fields plays a huge role in feeding the ground water of irrigated and adjacent territories. Groundwater is used for outflow and to a lesser extent for evaporation and transpiration. In the area of the bedrock bridge separating the Samarkand basin from the Bukhara oasis, in a significant part of the territory, ground water, approaching the surface, begins to be consumed for evaporation and their mineralization increases to 3-5-10 g/l.
The irrigation zone of the Bukhara region is located in the lower reaches of the Zerafshan River, south-west of the Khazarian Gorge. It covers the Bukhara and Karakul parts of the Zerafshan delta, as well as partially adjacent territories of the ancient Zerafshan outflow cone and wide-undulating plains and plateaus. At the exit from the Khazarian Gorge, Zerafshan forms a vast Bukhara subaerial delta, on which the floodplain of the river and two above-floodplain terraces stand out. The first above-floodplain terrace was formed on both banks of the river with a width of several meters to 2 km. Its excess over the water level is 1-1. The outflow of groundwater, which lies at a depth of 1-2 m and has an increased mineralization (5-10 g / L), is very weak. In terms of land reclamation, this is the most unfavorable part of Bukhara.
On a large area of the Bukhara part, alluvial deposits, represented by a layered complex of loams, sandy loams, sands and pebbles, are overlain by agro-irrigation sediments, the thickness of which in most cases exceeds 0.5-1.5 m. According to the mechanical composition, they are different, but medium and heavy loams predominate.
According to the conditions of groundwater flow, the Bukhara part as a whole belongs to a low-flow area. The inflow is about 4-5 times higher than the outflow. The main volume of water entering the oasis is spent on feeding groundwater, transpiration by vegetation and physical evaporation. Such an imbalance in the flow and flow of water causes the rise of groundwater and leads to the tension of the salt marsh process.
It is established that as the conditions of groundwater flow from the top of the delta to its periphery deteriorate, in addition to increasing the degree of groundwater mineralization, the type of mineralization changes from bicarbonate-sulfate to sulfate-chloride and even in some places chloride. The content of magnesium and alkalis also increases. The middle part of the delta is located hypsometrically below the upper one and has a flattened relief. It is composed of loamy alluvial deposits. Pebbles lie under the cover deposits at a depth of 5-10 m.
The outflow of groundwater is difficult. The depth of their occurrence in the predominant part of the territory is 1-3 m. The mineralization of groundwater is kept at the level of 2-5 g/l.
The peripheral (lower) part of the delta is characterized by an almost complete absence of surface slopes and poor drainage. The soils are composed of loam, with 5-10 m of fine-grained sand underlying.
The outflow of groundwater, which lies at a depth of 1-2 m and has an increased mineralization (5-10 g / l), is very weak. In terms of land reclamation, this is the most unfavorable part of Bukhara.
On a large area of the Bukhara part, alluvial deposits, represented by a layered complex of loams, sandy loams, sands and pebbles, are overlain by agro-irrigation sediments, the thickness of which in most cases exceeds 0.5-1.5 m. According to the mechanical composition, they are different, but medium and heavy loams predominate.
According to the conditions of groundwater flow, the Bukhara part as a whole belongs to a low-flow area. The inflow is about 4-5 times higher than the outflow. The main volume of water entering the oasis is spent on feeding groundwater, transpiration by vegetation and physical evaporation. Such an imbalance in the flow and flow of water causes the rise of groundwater and leads to the tension of the salt marsh process.
It is established that as the conditions of groundwater flow from the top of the delta to its periphery deteriorate, in addition to increasing the degree of groundwater mineralization, the type of mineralization changes from bicarbonate-sulfate to sulfate-chloride and even in some places chloride. The content of magnesium and alkalis also increases. A wide range of vertical altitudinal zoning-from the foothill plains to the middle categoriesdetermines vertical climatic zoning, which is manifested in a decrease in air temperatures and an increase in the amount of precipitation with increasing terrain height. The complex mountain-geomorphological structure determines frequent regional climatic features, different thermal resources on the territory and moisture content by precipitation.
In General, the climatic heterogeneity into the framework of conventional soil-climatic zoning, according to which the allocated zone with the climate of the mountain steppes, gray zone climate semiarid steppe and desert area with arid (desert) climate. In the desert zone, as well as in the belt of light and typical gray soils, the values of the average annual air temperature and the duration of active vegetation periods of non-heat-loving (above +5o) and heat-loving (above +10o) plants are very close to each other.
Against the background of minor differences between the lower vertical soil-climatic zones, as well as within the latter, individual massifs have different heat input. So, the belt of light serozems is noticeably warmer than the rest of the territory. The belt of typical serozems is the most variegated in this respect.
The Zerafshan Valley looks more moderate, where the average annual air temperature ranges from 12. Irrigation dramatically changes the water regime of soils. It makes it possible to maintain the soil in a moist state during the entire growing season. Therefore, the activity of microbes-mineralizers sharply increases and flows freely until the onset of low temperatures, limited only by the reserves of energy material in the soil (the content of organic substances). In the first years of irrigation, serozems are sharply depleted of humus and nitrogen. In the future, apparently, with a sufficiently deep occurrence of groundwater, humus reserves stabilize, and with the increase in the process of olugoveniya -increase.
Long-term irrigation is usually accompanied by soil compaction, and in monoculture, the destruction of microaggregates and the formation of crust after irrigation and precipitation.
On old-irrigated lands, the soil layer is gradually increased by silty material brought to the fields by irrigation water and large masses of earthy fertilizers. irrigated agriculture in the ancient oases of Uzbekistan has existed for more than 2 thousand years and the capacity of irrigation sediments reaches 1-2 m or more. Irrigation sediments are mostly high-carbonate (7-9% CO2) and contain a significant amount of organic substances (0.4-0.5% in suspensions of large channels and 0.6-0.9% in suspensions of ok-aryks). In addition, the sediments contain a significant amount of nitrogen, phosphorus and potassium. Cultural and irrigation horizons on unsalted soils are usually permeated by a dense network of earthworms, mainly earthworms, which improves the water-air properties of soils. In the conditions of modern irrigation agriculture, with proper soil treatment, the introduction of a large amount of mineral fertilizers, the fertility of ancient irrigated soils has significantly increased. Irrigation has a particularly great positive effect in the development of low-fertile desert takyr and gray-brown soils. According to many scientists [1][2][3][4][5][6], during soil researches in the thirties in left-bank part of the Bukhara oasis, along Zerafshan's course, on his elation were formed old irrigated (cultural and irrigation), meadow soils at a bedding of ground waters during the summer period at a depth of 3-5m. In the winter ground waters rose to 2-3m and in a certain measure influenced soil formation processes. Ground waters were generally fresh and low-mineralized. In right-bank part of the delta probably the soils irrigated meadow soils also dominated. There are no direct certificates on it, but soil shooting of 1963 has revealed the significant areas occupied with the soils which are old irrigated meadow soils in this part of the delta.
The profile of soils has been put powerful (1,5-2m) by the agro irrigational horizon which had the same light gray coloring. On mechanical structure of the soil were mainly heavy. On a soil surface as a result of her drying after watering the soil jointed crust was formed.
The maintenance of a humus in the arable horizon of these soils made 1,5-2,5%. In the below-lying horizons the quantity of a humus didn't go down to 2-2,5m lower than 0,5%.
The soils which are old irrigated meadow soils were mainly not salted and weakly salinized (the dense rest of 0,1-0,5%). Average salinized soils met much less often. The type of salinization was sulphatic.
In places in soils the weak salinized came to light in the analytical way, but morphologically it wasn't shown.
Only gross content of phosphorus and potassium is shown in [1,6] analyses provided in work. Their contents in an arable layer fluctuated respectively from 0,08 to 0,20% and from 1,01 to 2,63%. Thus, these soils were rich with reserves of potassium and are poor in phosphates. The maintenance of CO2 of carbonates on a profile fluctuated from 6,8 to 9,8%.
Along with the soils irrigated meadow soils in left-bank part of the delta meadow soils at a bedding of ground waters of 1-3 m were formed. They occupied the central part of the described territory along the canal Shakhrud and further all east suburb of the delta. They settled down on poorly raised relief elements among surrounding their superfluous hydromorphy soils and saline decreases. Meadow soils were old deposits with the agro irrigational horizon. The profile on mechanical structure was heavy, is more rare sandy loam.
Being formed at a close bedding of fresh or low-mineralized ground waters, meadow soils became covered by the violent vegetation promoting formation of a powerful turf (10-12 cm) with pronounced structure of soils. The maintenance of a humus in the cesspits horizon reached 3,5%. In the powerfully saline soils the vegetable cover was rare, a turf fragile and less powerful. The maintenance of a humus in her made 1,0-2,2%. Content of gross phosphorus in soils fluctuated in a profile within 0,168-0,117%, potassium -1,797-2,354%. The quantity of carbonates on a profile varied from 7 to 8% meadow alluvial soils in various degree were subject to salinization: from weakly salinized to average and the highly salinized. In the horizon the content of salts reaches 1,6-4,0%, in underlying -to 0,3-0,6%.
On Karakul part of the delta of Zarafshan before construction of the Amu-Karakul canal at a deep bedding of ground waters (3-5m) soils irrigated meadow soils developed [10]. They on properties were The humus horizon reached the power of 70-100 cm. The arable horizon of these soils contained 1,2-1,4% of a humus. It is much less, than in the cesspits horizon the old salinized structured meadow soils.
But it is clear, the humus which is contained in the 10-12cm cesspits horizon, was redistributed in an arable layer which power is 2-3 times more. Nitrogen soils have held 0,103-0,135%.
Gross phosphorus in soils there were 0,117-0,210% that exceeded his contents in initial soils a little.
In the melioration relation the old irrigated meadow soils became slightly better: among them the weakly salinized and washed-out soils prevailed, average salinized met seldom, highly salinized was almost not. Nevertheless, saline soils, quite considerable on the area met here. Along with development the rejuvenated meadow soils use meadow soils in the irrigated agriculture continued. There was probably a gain of the irrigated lands due to development of the new, earlier not mastered territories. Again developed soils have been also presented by generally old deposits.
The intensive use meadow soils under an irrigation has led almost to universal raising of ground waters that has caused return (the return evolution) speak rapidly the semi -hydro morphed soils in hydro morphed meadow.
Researches of 1963 have shown [8,11] that in a left bank of the Bukhara delta the small areas of the old irrigated meadow soils remained only in her upper courses and in the southern part, between Kagan and Bukhara, along the canal Sheihang. In right-bank part the soils which are old irrigated meadow soils have been widespread more widely -in Peshku, Shafirkan and Gizhduvan districts. But the prevailing space in right banks was occupied by the meadow alluvial soils which are mainly old irrigated. Also saline soils meadow met here.
In the territory of the Karakul delta of Zarafshan the soils which are old irrigated meadow soils evolved in the old irrigated meadow alluvial. A significant area was occupied here by meadow saline soils, and also very strongly salted deposits.
The old irrigated meadow alluvial soils of the Bukhara delta of Zarafshan which predecessors were soils irrigated meadow soils had (according to RPE of Uzgiprozem institute) the agro irrigational horizon with power from 1,0 to 2m. He was generally average salinized mechanical structure. The humus horizon reached 70-100cm. The maintenance of a humus and nitrogen in the arable horizon of these old irrigated meadow soils was lower (0,9-1,1% and 0,05-0,07%), than in the old irrigated meadow soils, and also in the old irrigated meadow soils which predecessors were rejuvenated meadow alluvial soils.
The melioration condition of the old irrigated meadow soils for the thirty-year period  has almost not changed. As old irrigated, meadow soils were generally not salted and weakly salinized and the old irrigated meadow soils which have come from them remained same, only the ratio not salted and weakly salinized became in favor of the last.
The old irrigated meadow alluvial soils of the Karakul delta of Zarafshan which predecessors were (meadow) soils which are also old irrigated meadow soils had less powerful agro irrigational horizon (70-100cm). His mainly average and easy mechanical structure power of the humus horizon made 50-70cm. It is slightly more humus and nitrogen in the arable horizon of these soils (0,9-1,3% and 0,08-0,12%), than in the old irrigated meadow soils of the Bukhara delta which have passed the same evolutionary way. Gross phosphorus there was also more (0,152-0,201%).
In the melioration relation the old irrigated meadow soils of the Karakul delta were much worse, than similar soils of the Bukhara delta. They were mainly average, met seldom and weakly salinized. There were few weakly salinized soils.
In general in 1963 in lower reaches to Zarafshan's valley the ratio between the old irrigated meadow soils of various extent of salinization looked as follows: not salted -18, weakly salinized -53%, the average salinized -28%, highly salinized -1%.
Researches of 1963 have shown that during 50 year period the soils which are old irrigated meadow soils in the considerable territory of the Bukhara delta have kept the substandard genetic level.
These soils had the powerful agro irrigational horizon. In different parts of the delta power varied him from 1 to 2m. The humus breeding at the same time changed from 50 to 100 cm. The maintenance of a humus in the arable horizon depending on his mechanical structure made from 0,7 to 1,5%. It is much less, than was with initial to the soil 50 years ago. Nitrogen in soils from 0,05 to 0,09%, gross phosphorus -from 0,114 to 0,168%.
The melioration condition of the soils which are old irrigated meadow soils has worsened a little.
Before the soil were mainly not salted and weakly salinized, now among these soils which no, aren't salted but have appeared together with weakly salinized soils of average and highly salinized. The ratio between these soils on extent of salinization was the following: the weakly salinized -80%, the average salinized -14%, the highly salinized -6%. On mechanical structure the old irrigated meadow alluvial soils having the powerful agro irrigational horizon mainly average structured, are more rare sandy. Sandy loam soils are dated generally for upper courses of water sources.
Humus breeding to 70-100cm. the maintenance of a humus in the arable horizons varies from 0,5 to 1,2%. Comparing these indicators to data of 1963, it is possible to notice that they are close to indicators on humus of meadow soils which predecessors they were meadow soils, and is much lower than indicators of traditionally meadow soils. Nitrogen the soil has held from 0,03 to 0,07%. Content of gross phosphorus fluctuates from 0,108 to 0,405%, mobile phosphates -from 4 to 15 mg/kg. Gross potassium in soils from 0,3 to 1,6%. In the maintenance of mobile forms of potassium also wide spacing -from 3-150 to 175-400 mg/kg of the soil. From these indicators it is possible to notice that the old irrigated meadow alluvial soils mobile forms both phosphorus, and potassium, are provided poorly. The same situation with batteries developed earlier.
Now the old irrigated meadow alluvial soils dominating in the lower part of the valley of river Zarafshan (The Bukhara and Karakul oases) in different degree are subject to salinization. Judging by the materials collected on four key farms, soils on extent of salinization are distributed as follows: weakly salinized -48%, the average salinized -29%, the highly salinized -23%. Thus, the melioration condition of modern soils of Zarafshan has considerably worsened in comparison with the last decades. Evolution of soils of Zarafshan took place at the standard, substandard, patrimonial and specific levels.
Virgin gray-brown soils from a surface aren't salted, but showed very low percents. Content of salts at a depth of 0,3-0,6 m reaches 1-2%.
The development of these lands which is followed by vegetative and washing waterings causes raising of ground waters to 3-4 m and evolution of automorphic gray-brown soils at the first stage of development in semi-hydromorphic gray-brown and meadow. On mechanical structure the new irrigated gray-brown and meadow soils sandy loam on sandy loam and sandy and sandy skeletal deposits. On a profile in them crystal of plaster and rare rusty spots meet.
The maintenance of a humus in the arable horizon new irrigated gray-brown and meadow soils varies from 0,4 to 0,8%, nitrogen -0,036-0,087%. Security of soils with mobile forms of phosphorus and potassium in the arable horizon low (respectively 12-27 and 50-200 mg/kg of the soil.
Carbonates in a profile of 5-6%. Soils are salted in weak degree, places washed out. Type of salinization of soils -chloride -sulfate.
Evolution of gray-brown soils takes place at the substandard, patrimonial and specific levels and looks as follows: VirCB-0 … → NewDСB-0 (1) → NewICM-1(0) analyzing evolution of the irrigated soils in lower reaches of the valley of river Zarafshan, within the Bukhara and Karakulsky oases, it should be noted that here the steady tendency of a hydromorphozation of soils prevails. It is promoted high extent of use of lands under an irrigation both insufficient natural and artificial fitness of the territory. Especially it belongs to average and lower parts of the Bukhara delta of Zarafshan and to Karakulskaya.
Increase of level of the mineralized ground waters above critical level causes salinization of soils, as is reflected in the scheme of evolution of soils for the 80's period. Sharp differences in salinization of soils of upper courses of the Bukhara delta, and also the Karakulsky delta are erased. All soils are almost equally subject to salinization processes. Also the irrigated gray and brown and meadow soils which are also transformed over time to meadow soil.
At the modern level of melioration of lower reaches of Zarafshan the above-stated tendencies will remain on prospect and the desertification of soils which is expressed in this case in salinization will progress.